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I Forge Iron

Why cant I drill into this metal?


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Made a pair of tongs out of rebar.  I've tried drilling the eyes for the rivet now that the tongs have cooled (air cooled).  I've got a new set of cobalt bits that refuse to bite in them.  I tried to drill a 1/8 pilot and it wont do anything.  I've got some 1/4 plate steel that the 1/8 bit slides right though.  Have I done something to the metal that has made it exceptionally hard?  Can rebar even get this hard?  I didn't quench it.  Not sure what's up.

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1 minute ago, Charles R. Stevens said:

Most of the rebar from the box stores comes from Mexico, they use rail and god only knows what in their mix. It tends to get very hard. Bridge and skyscraper drops are a better material. Tongs get hot, you need to cool them, even if you punch and drift the eyes, do you see the problem?

Sorry Charles.  I'm new to annealing and hardening metal.  I'm a woodworker masquerading as a smith.  : )   I didn't think I could get any  metal hard enough for cobalt bits to not do something to.  Did I do something wrong to make it this hard or was it that way before I started forging?

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Grade 60 rebar can easily get hard and brittle. Rebar does not have a specified chemical composition, only a minimal yield strength.

 

I made my first pair of tongs from grade 60 rebar. They came out fine, but when trying to cold set the bit just a small amount one side snapped. I arc welded the bit and still use the tongs.

You didn't do anything wrong, except for using rebar for tongs.:P. You may be able to anneal the tongs to drill the hole, or hot punch it, but that still leaves the problem that Charles pointed out with future quenching. I would recommend  hot punching the hole and using them, but do not be surprised if they snap on you at some point.

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You didn't do anything wrong, except not testing the mystery metal. Some steels will air harden (because of the "impurities" they quench in still air) and much of the stuff used in residential foundations is of that type. Rebar (and A36 structural steel) simply has to meet a performance specification, so it's not a known composition. 

Things to remember, don't use the slack tub to cool mystery steel, medium or high carbon steels. Rebar that gets hard in air is not going to live long when you cool it in water, and you will because the reigns are getting hot from holding a hunk of hot steel.  

Time to learn to hot punch steel...

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I've never used rebar but a rule of thumb you could apply when you want to drill any steel you suspect is harder than mild steel:

Put it in the fire, get it hot, turn off your blower & let the fire die with your piece of metal in the fire so it cools as slow as possible. Drill it later that day or the next day. Without getting all technical, that's basic annealing. Same goes for filing hard metals.

Annealing is like having a sauna. Quenching is like someone throwing a bucket of water over your head.

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